RbCs Project: News
Ground-state molecule paper published in PRL
December 2014

Our latest paper, Creation of Ultracold 87Rb133Cs Molecules in the Rovibrational Ground State has been published in the 19th December edition of PRL. In this paper, we present STIRAP transfer of 87Rb133Cs Feshbach molecules to the absolute ground state, and make measurements of the rotational splitting and electric dipole moment.

Hua is leaving!
September 2014

After a year, we must say goodbye to Zhonghua Ji. Hua joined us last year and has quickly learned the experiment and been instrumental in keeping it running and our recent experiments with ground state molecules. We all wish him the very best of luck in his new job in china.

Ground state molecules paper released
September 2014

Our latest paper, Creation of ultracold 87RbCs molecules in the rovibrational ground state, is on arXiv.

To the right is the final figure from the paper, showing the dramatic DC Stark shift of the STIRAP transitions. From this we calculate a molecular-frame electric dipole moment of 1.225(3stat)(8sys) D, and a maximum laboratory-frame dipole moment of 0.355(2)(4) D, which to our knowledge is the largest ever achieved in an ultracold molecule experiment.

High-voltage electrodes installed
June 2014

We have installed high-voltage electrodes in our system, to apply up to ±5kV. With this, we can reach DC electric fields of 1 kV cm-1. We will use these electrodes to measure the Stark shift of the molecular transitions and thus the permanent dipole moment of 87RbCs in the ground state.
Ground state molecules!
May 2014

We have transferred our 87RbCs Feshbach molecules to the rovibrational ground state! To the right, we see the number of remaining Feshbach molecules as they are transferred to the ground state and back. The solid and dashed lines are computer models of the Feshbach and ground states respectively, and give us a 50% one-way transfer efficiency.set are the pump and Stokes pulse sequences and the dependence of the transfer on the Stokes frequency. In the latter we observe only a single peak, corresponding to the mtot=5 lowest hyperfine ground state.

Spectroscopy of the RbCs ground state
February 2014

Spectroscopy of the Rovibrational ground state of RbCs! The pump laser is on resonance with the v'=29, J=1, Ω=1 state, removing the Feshbach molecules. As the Stokes laser reaches resonance with the J''=0, v''=0 ground state, we see the molecules form a dark state and stop decaying.

On the right, we see also the J''=2 state. This gives a rotational constant of 0.0163526(7)cm-1.

Pete, Stefan and Manfred go to YAO
March 2014

Pete went to YAO 2014 in Barcelona, with Manfred and Stefan. He gave a talk titled "Experiments with Ultracold RbCs molecules" (slides).

Michael passes his viva!
March 2014
Michael successfully defended his thesis on 6th March 2014. The title of his thesis is 'Creation of ultracold RbCs molecules'.
Excited state spectroscopy of RbCs
September 2013
We have found transitions to several vibrational and rotational excited states of our RbCs molecules. Here we see the transition to the v'=38, J'=3 state at 192560.49(2) GHz. This is the first of two transitions needed for STIRAP transfer to the ground state.
We have RbCs Feshbach molecules!
February 2013
Following our work on Cs2 Feshbach molecules, we have now created a cloud of around 5000 87RbCs molecules using the 197 G resonance. We sweep down to 181 G for Stern-Gerlach separation, then back up to dissociate. Next we will attempt this with 85RbCs in the current dipole trap, and install the new, larger trap. We are also currently designing a new laser setup for excited-state spectroscopy, in preparation for transfer to the ground state using STIRAP.
Lots of Cs2 Feshbach molecules
January 2013

Using the 19.8 G Cs Feshbach resonance, we have associated Caesium into Cs2 molecules. Then, using Stern-Gerlach separation, we pull the molecules out of the cloud and let them fall away, so we can make more! We have produced 30 clouds of molecules in this fashion, with 150-3000 molecules each.

STIRAP lasers locked to ULE cavity
January 2013

The new cavity from ATFilms is now installed, aligned and both lasers are locked to it. The finesse is 18,200 at 980 nm and 11,200 at 1550 nm. This cavity will form the stable reference for the lasers for STIRAP, to transfer molecules into their ground state.

BEC back in the RbCs lab!
November 2012
After 12 months of working with a mixture of 85Rb and 133Cs we have now switched our experiment back to produce ultracold mixtures of 87Rb and 133Cs. The first step in the optimisation process is the production of a 87Rb BEC in a single beam hybrid trap. Currently we produce condensates containing ~106 atoms. We're now implementing our levitated crossed dipole trap in order to load and sympathetically cool 133Cs in the absolute internal ground state.
Dan passes his viva!
September 2012
Dan successfully defended his thesis on 28th September 2012 and has now completed his PhD. His thesis titled 'Feshbach spectroscopy of an ultracold Rb-Cs mixture' is available here.
Theoretical two-species BEC paper submitted
September 2012
A theoretical paper investigating our two-species BEC results (D. J. McCarron et al., Phys. Rev. A 84, 011603(R) (2011)) has now been submitted. This work obtains time-independent solutions of the trapped two-species condensate through zero-temperature mean-field simulations. The results are sensitive to experimentally relevant shifts in the potentials which give rise to a range of possible structures, including `ball and shell' formations, good overall agreement with the experimental results is found for all regimes. This work is a collaboration with Tom Billam of the University of Otago and Robert Pattinson, Nick Parker, and Nick Proukakis of both Newcastle University and the newly formed Joint Quantum Centre (JQC) Durham-Newcastle. The manuscript is available on the arXiv.
85Rb-133Cs paper submitted
August 2012
Details of our 85Rb-133Cs work can now be found in our paper, "Feshbach spectroscopy of an ultracold mixture of 85Rb and 133Cs". Here we measure 14 interspecies resonances in the lowest spin channels between 0 and 700G. For this system the interspecies background scattering length is close to zero over a large range of magnetic fields, permitting the sensitive detection of Feshbach resonances through interspecies thermalisation. Our results confirm the quality of the Rb-Cs potential curves and offer promising starting points for the production of ultracold polar molecules.
Visit to Taiwan and Japan
June 2012

Simon and Danny have recently visited research groups at the National Tsing Hua University (NTHU) in Hsinchu and the Institute of Atomic and Molecular Sciences (IAMS) in Taipei as part of an exchange scheme run by the Royal Society. The purpose of this visit was to share ideas and experience of working with ultracold mixtures while taking the opportunity to learn about, and get some hands on experience with, frequency combs. While visiting these groups Simon gave a talk (which was briefly interrupted by a 'small' earthquake at NTHU!) titled "Bose-Einstein condensation with tunable interactions: from solitons to molecules".

While in Asia Simon and Danny then travelled to Kyoto, Japan to visit Yoshiro Takahashi's group at Kyoto University. Here insight of working with ytterbium was gained which will be invaluable for the YbCs project. From Kyoto Simon and Danny then took a bullet train to Tokyo covering the 300 miles in 2 hours 45 minutes! In Tokyo they visited Shin Inouye's group at The University of Tokyo to learn about their experiment that produces K-Rb molecules in the rovibrational ground state via photoassociaiton and STIRAP. Importantly this group uses an ultrastable ULE cavity to frequency stabilise their STIRAP lasers in a scheme similar that which will be employ in our experiment. When visiting these groups Simon presented a talk on our work titled "Towards ultracold heteronuclear RbCs molecules ".

Finesse of the home built cavity
May 2012
The Finesse of the cavity is measured by sweeping across a cavity resonance and recording the decay time of the light field inside the resonator. The Finesse for all relevant wavelength for the STIRAP transfer of RbCs is >3000 and thus in the expected range. The cavity length of 20 cm gives a free spectral range of 750 MHz. A finesse of 3000 results in a full width half maximum of 250 kHz of the cavity peaks.

Intra- vs Interspecies Resonances
May 2012

The figure shows an intraspecies 85Rb resonance near 369G neighbouring an interspecies resonance close to 370G. Closed (open) symbols indicate 85Rb (133Cs) data. Loss of 85Rb atoms from the trap reveals the presence of both resonances. Temperature data allows the resonances to be distinguished as either intra-or interspecies. The 133Cs temperature is unchanged at the 85Rb alone resonance as there is no significant change in the interspecies collision rate. In contrast to this, at the interspecies resonance at higher field the inelastic collision rate increases dramatically and results in 85Rb sympathetically cooling the 133Cs.

85Rb-133Cs bound state spectrum
April 2012

In parallel to our Feshbach spectroscopy of a 85Rb-133Cs mixture the group of Jeremy Hutson calculated the s-wave interspecies scattering length and weakly bound molecular states for the same field range of 0 to 700G. The results of their coupled channel calculations are shown here alongside our experimental results. Bound states arising from L = 0 (s states) are shown as black lines while those from L = 2 (d states) are shown in other colors that indicate the value of MF (see figure). The bound-state energies are plotted relative to the energy of the lowest hyperfine state of 85Rb + 133Cs, the (2,2) + (3,3) hyperfine level. Resonance positions are marked on the scattering length plot using vertical lines of the same color as the corresponding bound state. The grey shaded region indicates where |a| < 30 bohr, here we observe thermailsation between the two species. All the bound states shown are for Mtot = 5, corresponding to s-wave scattering in the lowest channel. Very good agreement is observed between the experimental and calculated Feshbach spectra.

Michael and Kirsteen attend YAO
March 2012

Michael and Kirsteen attended the eighteenth Young Atomic Opticians Conference in Krakow. Here Michael gave a talk on our work titled 'A quantum degenerate mixture of Rb and Cs: Towards ground state heteronuclear molecules' and Kirsteen presented a poster titled 'Towards a quantum gas of polar YbCs molecules'. Further information and photographs of the fun and games can be found here.

Feshbach spectroscopy of an ultracold mixture of 85Rb and 133Cs
March 2012

We have observed interspecies Feshbach resonances in an optically trapped mixture of 85Rb and 133Cs. We measure 14 interspecies features in the lowest spin channels for a magnetic field range from 0 to 700G which are in are in good agreement with coupled-channel calculations.

This system has an interspecies background scattering length that is close to zero over a large range of magnetic fields, permitting the sensitive detection of Feshbach resonances through interspecies thermalisation as shown in the plot below. Here closed and open symbols indicate the 85Rb and 133Cs temperatures respectively. Off resonance the temperature difference between the two species arises from a combination of the small interspecies background scattering length and the differing trap depths for the two species in the optical trap. In regions near broad Feshbach resonances, such as near 110G and 610G, multiple resonances are only identified by studying the variation in the atom number.

Visit to Innsbruck, Austria
November 2011
Kirsteen and Michael went to visit the ultracold atom experiments at the University of Innsbruck, as well as those at the Institute for Quantum Optics and Quantum Information. Whilst there, Kirsteen gathered information on how to design Zeeman slowers and vacuum systems, similar to those being planned for the YbCs experiment, whilst Michael learned some technical details about the STIRAP process and about working with Cs at high magnetic fields.
Observation of 87Rb-133Cs resonances
October 2011

We have observed interspecies Feshbach resonances in our optically trapped mixture of 87Rb and 133Cs in the F=1, mF=+1 and F=3, mF=+3 states respectively. Initially to test the experimental protocol previously observed resonances were measured at 181.56(6)G, 197.16(2)G and 352.6(1)G in good agreement with previous work. The search was then extended to magnetic fields greater than 400G guided by theoretical calculations by the group of fellow AtMol member Jeremy Hutson.

Three new interspecies Feshbach resonances have been observed at 789.7(2)G, 910.3(1)G and 1115.2(3)G in good agreement with theoretical predictions. The 133Cs number measured across the 1115.2(3)G resonance is shown in the plot. The red dashed line marks the theoretical resonance position and the purple dotted line marks the zero-crossing in the scattering length.

STIRAP Cavity Construction
August 2011

Work has begun on the cavity that will be used to lock the two lasers required for the STIRAP optical transfer. The mirrors for the cavity consist of one plane mirror and one spherical mirror with a radius of curvature of 50cm. The reflectivity of both mirrors is >99.91% which allows a cavity with a finesse of ~3000 to be made.

The blue line in the figure shows the signal from a commercial etalon (Coherent, 33-6230-001) with a 300 MHz free spectral range (FSR). The red line shows the signal from a home made cavity consisting of the plane and spherical mirrors separated by ~20cm. Using the signal from the commercial etalon the FSR of the home made cavity was measured to be 768(5)M MHz. This corresponds to a calculated mirror separation of 19.5(1) cm in good agreement with what we measure in the lab.

The next step is to secure these mirrors onto either end of a 20 cm long Zerodure spacer. A PZT will be placed between one mirror and the spacer to allow the cavity to be locked to a Pound-Drever-Hall signal from a frequency stabilised 852 nm laser.

Danny submits his thesis
July 2011
Danny has now submitted his PhD thesis titled A Quantum Degenerate Mixture of 87Rb and 133Cs. Here changes made to the orginal RbCs setup are described and results obtained using the hybrid trap are presented. Significant results include the discovery of a new route to Cs BEC via sympathetic cooling with Rb and the production of dual-species BEC. Danny now waits to be examined in the upcoming months to complete his PhD.
Evaporative cooling of 133Cs around 22G
June 2011
The evaporation of 133Cs alone in the crossed dipole trap in the F=3, mF=+3 state was investigated for bias fields between 5G and 45G. For each bias field the levitated crossed dipole trap depth was reduced from 69 µK to 1.9 µK in 2.6 seconds. The remaining atom number and temperature were used to calculate the final phase-space density in the trap and the efficiency of the evaporation. The results of this investigation are shown in the figure and agree very well with expected results using the theoretical scattering length data provided by P. Julienne and co-works at NIST (bottom plot). When the scattering length is very small, near the zero-crossing at 17G, the elastic collision rate is too low for efficient rethermalisation. However when the scattering length is large, at Feshbach resonances (dashed lines), inelastic collisions greatly reduce the trap lifetime of the sample. For efficient evaporation the elastic collision rate must be significantly greater than the inelastic collision rate. This occurs when the scattering length is small, ~200-400a0 where a0 is the Bohr radius 0.0529 nm.

We have located two regions where the evaporation efficiency ~3 (purple dashed boxes), here subsequent evaporation by titling the trap with the magnetic field gradient can lead to the production of 133Cs condensates containing up 8x104 atoms. One region is the standard window used to produce 133Cs BEC located between 20-25G. The second window spans 18G to 19.6G and marks the discovery of a new bias field region where Cs BEC can be achieved.

Fibre laser repaired and realigned - BEC achieved
April/May 2011
Our IPG fibre laser has now been repaired and returned to the lab. The original dipole trap setup has been realigned and can be operated two configurations. The first uses a single dipole beam with axial confinement provided by a magnetic field gradient. The second uses two crossed dipole beams which allows the magnetic field to become a free parameter.

To align the crossed dipole trap both beams were aligned independently using the single beam configuration. As this trap can only confine low field seeking states atoms in this trap are prone to Majorana losses if the dipole beam is aligned through the magnetic field zero. This loss was used to locate the magnetic field zero in the vertical and horizontal directions as shown in the figure. The two data sets shown correspond to the alignment of each dipole beam with a power of 6 W. The fits to these data are to guide the eye.

Once the magnetic field zero was located each dipole beam was positioned 200 µm below the magnetic field zero. Bose-Einstein condensates consisting of 2x106 87Rb atoms can now be made in either single beam trap while 87Rb condensates of 2x106 atoms and 133Cs condensates consisting of 8x104 atoms can now be made in the crossed dipole trap.

For details on the experimental procedures followed to reach these results please see our recent publications.

Dual-species BEC paper published in PRA
April 2011

Phys. Rev. A 84 011603 (2011); arXiv:1102.1576

We report the formation of a dual-species Bose-Einstein condensate of 87Rb and 133Cs in the same trapping potential. Our method exploits the efficient sympathetic cooling of 133Cs via elastic collisions with 87Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. The two condensates each contain up to 2x104 atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the 87Rb during the cooling, we create single-species 133Cs condensates of up to 6x104 atoms.

For more information see Publications.

Simon speaks at EuroQUASAR meeting
March 2011
Simon recently travelled to Obergurgl, Austria to attend the EuroQUASAR meeting titled Frontiers of Matter Wave Optics. Here he presented a talk on our recent work titled A Quantum Degenerate Mixture of 87Rb and 133Cs.

Details on this significant result can be found in one of our recent publications Phys. Rev. A 84 011603 (2011).

Sympathetic Cooling within the quadrupole trap improved
March 2011
Magnetic trap loading has been improved leading to an increase in the number of 87Rb that we are able to trap. We are now able to capture up to 7x10^8 87 Rb atoms, allowing for faster, more efficient forced RF evaporation.

This has had a marked effect on sympathetic cooling of 133Cs, which we are now able to cool with only a small deviation of the 87Rb number from the single species case. After the RF evaporation we obtain a similar number of Cs atoms, at a phase-space density which is an order of magnitude higher than previously.

The figure highlights the atom number remaining in the trap at different temperatures within the RF evaporation sequence. Green squares highlight 133Cs data points, solid red circles highlight 87Rb cooling Cs data, and hollow purple circles correspond to the single species 87Rb case. The grey data points highlight previous data. All lines have been added to guide the eye. Notice how the 87Rb cooling Cs case differs little from the single species case, whilst previously there was a drastic difference. It can also be observed that it is possible to cool the 133Cs to lower temperatures now.

2 Papers accepted for publication in Eur. Phys. J. D
January 2011
Recent results involving BECs of Rb and Cs have been accepted for publication in Eur. Phys. J. D. The first of the two papers focuses on the technical aspects of the experiment and discusses the combined magnetic and optical potential in depth. We also report on Bose-Einstein condensation of 87Rb in the levitated crossed dipole trap, as well as sympathetic cooling of the different m_F sublevels. Finally the paper discusses the applicability of the apparatus to sympathetic cooling of 133Cs.

The second paper is concerned with the condensation of 133Cs via sympathetic cooling with 87Rb. We then report the production of simultaneous 87Rb and 133Cs BECs and the formation of Cs2 molecules.

The figure, taken from the 87Rb BEC paper, highlights the sympathetic cooling of the m_F=-1 and m_F=0 states of 87Rb, after rethermalising elastic collisions with atoms in the m_F=+1 state. Figure (a) demonstrates how the temperatures of the 0 and -1 states follow that of the +1 state after collisions. The inset presents the potential for each state. Here solid lines correspond to the trap depths, the dashed line corresponds to the trap depth along the beam and points correspond to temperatures from measurements. Figure (b) demonstrates how well sympathetic cooling works, as only the +1 atoms are lost initially, due to efficient sympathetic cooling. Once all +1 atoms are lost the m_F=0 atoms take over as the refrigerant and cool the -1 atoms. Solid lines are added to guide the eye.

To read the abstracts, see Publications.

EuroQUAM conference "Cold Quantum Matter: Achievements and Prospects"
September 2010
Simon, Michael, Hung Wen and Danny travelled to Ischgl in Austria to attend the concluding EuroQUAM network meeting on 'Cold Quantum Matter'. A stimulating program consisting of 7 keynote lectures and 23 talks spanned four days in the Austrian mountains. To match the high standard of research presented the conference was held at Austria's highest conference centre, the Pardorama located at an altitude of over 2600m! The construction of this building is very unusual, the steel frame alone weighs over 1300 tonnes and yet it rests on the mountain top at just three points!
Danny visits St. Andrews
September 2010
Danny recently attended the Uk Cold-atom/Condensed Matter Network annual meeting held at St. Andrews University. Here he gave a talk presenting results from the lab including the two-species BEC data, the production of Cs Feshbach molecules and the observation of an interspecies Feshbach resonance. While in St Andrews he was able to visit Donatella Cassettari's group, here they are building a 6Li-87Rb experiment and are developing novel optical traps using computer generated holography.
Interspecies Feshbach Resonance
September 2010
We have observed our first interspecies Feshbach resonance in an optically trapped Rb-Cs mixture. We prepare 2.2x104 Cs atoms as a probe species in a collisional bath of 3.3x105 Rb atoms, both species have a temperature of 300nK. We allow the mixture to evolve for 5 seconds at a specific magnetic field value and monitor the Cs atom number as a function of the magnetic field. An enhancement of the trap loss of our probe species reveals the location of the Feshbach resonance. We measure the resonance to be located at 181.7(5)G and the width to be approximately 3G. These values compare well to previous work.
Observation of Feshbach molecules
August 2010

We can create Cs Feshbach molecules by applying a magnetic field sweep across a Feshbach resonance to a high phase-space density sample of Cs atoms. We use a Feshbach resonance located at 19.8G and observe molecule production from either a Cs Bose-Einstein condensate or a high phase-space density thermal cloud. The molecular sample is distinguished from the atom cloud via spatial Stern-Gerlach separation. In the image a magnetic field gradient levitates the atom cloud while the molecules accelerate downward at approximately 0.6g.

To image the molecular cloud a reverse field sweep across the Feshbach resonance is applied. This brings the molecules above the scattering continuum and results in them quickly dissociating back into free atoms. An absorption image of the reconverted atoms then reveals the spatial distribution of the molecules. By levitating the molecules we are able to measure the molecular magnetic moment. We find that µ = 0.92(1) µB, which is in good agreement with previous data.

Immiscibility in a Two-Species Bose-Einstein Condensate
July 2010
We can make a dual-species Bose-Einstein condensate with Cs and 87Rb in a levitated crossed dipole trap. To load both species into the dipole trap we have slightly but significantly changed the final RF evaporation strategy with respect to that used to make the Cs BEC. Typically we load 3.5x106 87Rb atoms and 7.1x105 Cs atoms at T = 12 µK into the dipole trap. The spin of both atoms is then flipped adiabatically and a 22.7 G bias field is applied. Further evaporation in the optical trap, by reducing the powers of the dipole trap beams and then by increasing the axial field gradient to 31.7 G/cm is then performed in 5.5 seconds. We can make dual-species condensates containing ~ 2x104 atoms of each species. At this bias field we observe immiscible behavior via a dramatic spatial separation of the condensed fractions of each species. This behavior is shown in the figure on the right. (a) Absorption image of a two component 87Rb cloud after a 20 ms TOF. (b) Absorption image of a two component Cs cloud after a 15 ms TOF. (c) Superimposed horizontal cross sections of each cloud clearly demonstrate the spatial separation of the two condensates. As expected this repulsive behavior is not observed between the thermal atoms present in each cloud.
June 2010
We have observed the first Cs Bose-Einstein condensate in our levitated crossed dipole trap. We load 2x108 87Rb atoms in F=1, mF=-1 and 2x107 Cs atoms in F=3, mF=-3 into a magnetic quadrupole trap from a UHV MOT. When the axial magnetic field gradient is 187 G/cm T = 160 µK, the Cs PSD ~ 10-7. RF evaporation of the Rb atoms enables the sympathetic cooling of Cs. After 38 seconds of RF evaporation NRb= 4.0x107, NCs= 1.4x107, T = 60 µK and the Cs PSD ~ 10-5. We then transfer 15% of the Cs atoms into a crossed dipole trap by ramping the axial field gradient down to 29 G/cm. Here T = 10 µK and the Cs PSD ~ 10-2. Simultaneously the spin is adiabatically flipped into F=3, mF=+3 and a bias field of 22.7 G is applied. Evaporative cooling, by reducing the power of the dipole trap beams and then increasing the axial field gradient to 34.0 G/cm, over 17 seconds enables us to reach BEC. The onset of BEC is observed with N ~ 105, typically we make pure Cs condensates containing ~3x104 atoms.
BEC of 87Rb.
March 2010
On March 6th 2010 we observed the first Bose-Einstein condensation of 87Rb in our setup. Our experimental sequence begins with the collection of ~4x108 87Rb atoms in a magneto-optical trap (MOT) loaded from a pyramid MOT source. The atoms are then optically pumped into F=1, mF=-1 state and transferred into a magnetic quadrupole trap, the field gradient is ramped up to 187 G/cm. At this point a 3.5 W dipole beam is switched on, the beam waist is 65 microns. This configuration provides a trap ~50 micro Kelvin deep, the magnetic gradient provides axial confinement. Forced RF evaporation is performed in the quadrupole trap until Majorana losses become significant. The dipole trap is then loaded by ramping down the magnetic potential to 29 G/cm. We typically load 5x106 atoms at ~5 µK. We evaporativley cool to BEC by reducing the trap depth to 3 µK over 23 seconds. On first observation our condensate atom number is ~2x105. By changing the final value of the trap depth we are able to control the condensate fraction that we obtain. This is shown in the figure on the right.
(a) If the trap depth is reduced to 6 µK the critical temperature, Tc = 350 nK. We obtain 1x106 atoms at 370 nK, this corresponds to a phase space density of 0.93.
(b) When the final trap depth is 5 µK Tc = 280 nK. We observe a bimodal distribution containing 7x105 atoms, the temperature is 250 nK and we measure a condensate fraction of ~15%.
(c) If the trap depth is ramped down to 3 µK Tc = 160 nK. For this final depth we measure a nearly pure condensate containing 2x105 atoms.
Loading Cs into the Dipole Trap
January 2010
This video shows the final 500ms of the dipole trap loading process. During these final stages the gradient of a quadrupole trap is ramped down from 45G/cm to 30G/cm in the presence of the dipole beam, this occurs during the first second of the video. Now the magnetically trapped Cs atoms are no longer supported against gravity and fall away leaving just the optically tapped Cs atoms.
Evidence of optically trapped Cs!
December 2009
The new 30W IPG fibre laser has been fully tested and inserted into the mixture setup. In the image the thin line indicates the optically trapped Caesium, trapped in the 150 micron waist of the dipole trap beam. At the bottom of the image those atoms that weren't optically trapped can be observed falling under gravity.
Science MOT Optimisation Complete.
August 2009
Optimisation of both Cs and Rb science MOTs has been completed. The image is of approximately 4x10^8 cold 87Rb atoms! See the Gallery for more images.
New research grant funded!
July 2009
More good news! EPSRC announce that our recent grant application entitled "A Quantum Gas of Ultracold Polar Molecules" will be funded (EPSRC Grant EP/H003363/1). The grant provides funding to implement the next phase of our mixture experiment - namely the creation of deeply bound and ground state heteronuclear molecules via magneto-association on a Feshbach resonacne followed by STIRAP transfer. Theoretical support and input will be provided by Jeremy Hutson's group in the Department of Chemistry.
Patrick successfully defends his thesis.
6 July 2009
Patrick Tierney has completed his PhD and passed his viva on 6 July 2009. His thesis, entitled "Magnetic trapping of an ultracold Rb-Cs atomic mixture" is available here.
Congratulations and well done!!
EuroQUAM satellite meeting on "Cold and Ultracold Molecules"
18 April 2009
We had the pleasure in organising and hosting a one day EuroQUAM satellite meeting on "Cold and Ultracold Molecules" following the 142nd Faraday Discussion also held in Durham on the same topic. The meeting was attended by around 60 scientists from throughout Europe involved in the ESF Cold Quantum Matter (EuroQUAM) EUROCORES Programme. A full day of stimulating talks saw each of the six collaborative research projects with the EuroQUAM programme represented, as well as two keynote talks given Jun Ye from JILA and Paul Julienne from NIST.

The programme of talks can be downloaded here and full details of the meeting together with the talk abstracts can be downloaded here.
As part of the laboratory tours we also presented a poster on the latest research developments on our mixture project.
New Coil Setup Tested
March 2009
The new coil setup has been assembled and tested. The bias fields and field gradients produced by the coils compare very well to the theoretical values. It is possible to produce a bias field of 1157G by running two bias coil pairs in series at 425A with 12V dropped across the coils.
QuDipMol Workshop - Innsbruck.
29/30 September 2008
Danny and Simon travelled to Innsbruck for a network meeting and workshop of the QuDipMol collaborative research project. The stunning mountain views were surpassed by the stunning results on the production of ultracold ground state molecules! Indeed the last couple of months have witnessed several major advances in this field, nicely summarised in a recent APS Physics Viewpoint article - From atoms to molecules (and back).
Publication of modulation transfer spectroscopy paper

September 2008: Our recent work involving modulation transfer spectroscopy has now been published in Measurement Science and Technology, Meas. Sci. Technol. 19, 105601 (2008). This work demonstrates that both the gradient and amplitude of modulation transfer spectroscopy signals, for the 87Rb F = 2 to F' = 3 and the 85Rb F = 3 to F' = 4 transitions, can be significantly enhanced by expanding the beams, improving the signals for laser frequency stabilization. The modulation transfer signal for the 85Rb F = 2 to F' transitions is also presented to highlight how this technique can generate a single, clear line for laser frequency stabilization even in cases where there are a number of closely spaced hyperfine transitions.

The figure shows a comparison between (a) modulation transfer spectroscopy and (b) frequency modulation (FM) spectroscopy for the 87Rb F = 2 to F' and 85Rb F = 3 to F' transitions at a modulation frequency of 12.35 MHz. The reference saturation absorption/ hyperfine pumping spectroscopy signal is shown in (c). This figure shows that, unlike FM spectroscopy, modulation transfer spectroscopy has one large zero crossing corresponding to the closed transition and a flat background signal.

Margaret successfully defends her thesis.
4 July 2008
Margaret Harris has completed her PhD and passed her viva on 4 July 2008. Her thesis, entitled "Realistion of a cold mixture of rubidium and caesium" is available here.
Well done!!
Observation of Cs Feshbach resonances.
November 2007
We have observed two d-wave Feshbach resonances in collisions between Cs atoms at around 118 G and 133 G. These resonance have been studied in previous work, but allow us to test the sensitivity of our measurement procedure before proceeding to search for interspecies Feshbach resonances.
Magnetic trapping of a cold Rb-Cs atomic mixture.
November 2007
We have submitted a paper to the Journal of Physics B: Atomic, Molecular, and Optical Physics which describes our experimental apparatus and recent studies of Rb-Cs mixtures. The full text of the paper may be downloaded from the arXiv. A key element for optimising the two-species MOT was the development of a novel technique for limiting the interspecies loss rate by spatially separating the two trapped atom clouds during loading. Figure (a) shows the loading of the two MOTs with (red line) and without (black line) the Rb MOT displaced. In both cases the Cs MOT is switched on after 40 s of loading Rb alone. Figures (b)-(e) show images and cross-sections of magnetically-trapped Rb and Cs atom clouds loaded from ordinary and displaced MOTs.
Update: January 2008
The paper has now been published by J. Phys. B and may be found here.
QuDipMol - Collaborative Research Project is funded!
May 2007
ESF announce that our European Collaborative Research Project on "Quantum-degenerate dipolar gases of bialkali molecules (QuDipMol) is one of six projects funded under the EuroQUAM programme. Led by Matthias Weidemuller (Albert-Ludwigs-Universitat, Freiburg) the project involves seven other groups whose prinicpal investigators are Hans Peter Buchler (University of Innsbruck), Simon Cornish (Durham University), Olivier Dulieu (Universite d'Orsay, Paris), Jeremy Hutson (Durham University), Hanns-Christoph Nagerl (University of Innsbruck), Giacomo Roati (University of Florence), and Pavel Soldan (Czech Technical University, Prague). The Durham component of this project is funded by EPSRC Grant EP/E041604/1.
Margaret in Munich
February 2007
In order to gain information about creating a stable optical dipole trap with a Nd:YAG laser, Margaret visited the Rb molecular BEC experiment run by Dr. Stephan Dürr at MPQ-Garching (photo, top left). Discussions with lab members yielded useful information about beam alignment procedures, safety, and intensity control, as well as updates on their recent experiments using Feshbach resonances to create and study 87Rb molecules.
Later in the week, she visited the Fermionic Quantum Gases project led by Dr. Kai Dieckmann at LMU- Münich to learn more about their three-species ultracold mixture. The photo (bottom left) shows five of the 14 lasers they use to reach the quantum degenerate regime in 87Rb, 40K, and 6Li. Discussions with Dr. Dieckmann and graduate student Matthias Taglieber provided a deeper appreciation of both similarities and differences between their Fermi-Fermi mixture and the Bose-Bose mixture at Durham. The trip was funded by the QUDEDIS short visit scheme.
Magnetically trapped Cs Atoms.
February 2007
The image shows MOT recapture of magnetically trapped Cs atoms. The green trace is the Cs fluorescence photodiode signal. The blue trace is the baseball coil hall sensor signal (proportional to the baseball current). The recaptured atom signal is approximately 8 mV, corresponding to 14% of the atoms initially loaded in the MOT being recaptured from the magnetic trap. The trap is turned on to a bias field of 51.2 G, avoiding known Cs Feshbach resonances. 35% of the loaded atoms remain after 40s, almost certainly limited by spin changing collisions.

Two species 2nd MOT demonstrated.
November 2006
The image shows the final beam alignment of the Durham 87Rb-133Cs mixture. The blue (red) lines are the Rb (Cs) 2nd MOT beam paths. The purple line is the probe beam path along the axis of the science cell.

Observation of Inelastic losses in a two species magneto-optical trap (MOT).
June 2006
The image shows the first two species fluorescence measurements of the Durham 87Rb-133Cs mixture. The blue (red) line is the measured fluorescence of the Cs (Rb) pyramid MOT, with no Rb (Cs) MOT repumping light present. The black line is the loading of the Cs MOT with no Rb repumping light present initially, but with the Rb repumping light unblocked after approximately 20 seconds. The number of atoms in the Cs MOT drops by approximately 20% in the presence of the Rb MOT. This is due to inelastic interspecies collisions in the pyramid MOT. We do not see a comparable drop in the number of trapped Rb atoms in the presence of Cs.
Patrick in Innsbruck
April-May 2006
In order to gain knowledge of the experimental techniques used within the ultra-cold atoms and quantum gases group at Innsbruck Patrick visited the experiments led by Prof. Rudi Grimm and Dr. Christoph Nägerl at Innsbruck. The visit was funded by the QUDEDIS short visit scheme. The majority of the time was spent in the laboratories of two experiments which employ optical dipole trapping of magnetically levitated Cs. These are the LevT experiment in which Cs was first cooled to quantum degeneracy, the subject of Jens Herbigs thesis (pictured far left alongside Patrick),
and the next generation Cs III experiment in which Cs will be trapped in a three dimensional optical lattice. The two graduate students on this experiment; Mattias Gustavsson (pictured left) and Elmar Haller, demonstrated how the various steps of cooling and trapping of Cs are incorporated into the experimental apparatus.
Cold Cs Atoms at Durham University!
September 2005
Today Cold Cs atoms were trapped in pyramid MOT for the first time. The MOT is the cloud of atoms just to the right of the hole in the centre of the image. The other five clouds are reflections of the MOT image in the pyramid optics.

Updated by Simon L. Cornish, May 2010